This invention relates to methods for improving the odor, color and fabric softening properties of N-higher alkyl-1,3-propylene diamines and of fabric softening compositions incorporating the improved N-higher alkyl propylene diamines.
The use of synthetic detergent compositions in heavy-duty household laundering has become a widespread practice. The formulations conventionally employed generally comprise synthetic detergent surfactants and alkaline builder salts which function to enhance the cleaning levels of synthetic materials. Some inorganic builder materials present in detergent formulations have been known to have a tendency to react with the metal ions present in the washing solution, precipitating out insoluble salts which deposit on the textile material being laundered. Such deposited mineral salts give the laundered fabrics a poor boardy feel, particularly at those areas of the fabric which are exposed to frictional and creasing effects such as collars and cuffs. This poor hand of laundered fabrics and resulting discomfort during use have in part resulted in the creation of a large and expanding market for softener formulations capable of improving the softeness or "hand" of laundered textiles. It has been found that the treatment of such materials with softening agents improves their softness of feel and may prolong the useful life of the textile materials. In addition, it has been found that such treatment generally results in a fabric having a reduced tendency to accumulate electrical charges, which fact facilitates the ironing of treated materials.
N-higher alkyl-1,3-propylene diamines are valuable softening agents and are compatible with most synthetic detergent formulations. However, heretofore they have not won much acceptance for use as fabric softeners, because the generally available technical grade N-higher alkyl-1,3-propylene diamines are characterized by an unpleasant odor which cannot be masked by the detergent perfumes currently available.
Additionally, the technical grade N-higher alkyl-1,3-propylene diamines have a tendency to discolor synthetic fabrics such as polyamides, polyesters, and the like regular household laundry; this discoloration darkens upon aging. The best explanation for the discoloration is that it is a heavy metal (e.g., iron) catalyzed decomposition of the diamine, which is a known heavy metal scavenger and used as such in the oil industry.
Presently, one of the best known methods for improving the properties of technical grade N-higher alkyl propylene diamines is by vacuum distillation. However, this method is expensive and relatively ineffective; the resulting diamine is not improved significantly, and it is prohibitively expensive for use in detergent formulations. In tergitometer tests using a commercially available household laundry detergent, no significant difference between the crude and distilled diamine was found. Nylon cleaning was particularly poor.